1. Field
The invention relates to a device for evaluating crystallinity, and a method of evaluating crystallinity.
2. Description of the Related Art
A thin-film transistor (“TFT”) is a type of field effect transistors, which is produced by depositing thin films of semiconductor on an insulative supporting substrate. Similarly to other field effect transistors, a TFT has three terminals, i.e., a gate terminal, a drain terminal and a source terminal. One of main functionalities of a TFT is switching operation. A TFT is used in sensors, memories, optical devices, etc. In flat display devices, a TFT is used as a pixel switching element or a driving switching element.
As displays become larger and have increased quality, such elements are also required to have increased performance. Accordingly, a technology to produce a high-performance TFT having higher electron mobility than an amorphous silicon TFT having an electron mobility from 0.5 cm2/Vs to 1 cm2/Vs. In this regard, a polycrystalline silicon TFT (poly-Si TFT) exhibits much higher performance than existing amorphous silicon TFTs. As a polycrystalline silicon TFT has an electron mobility ranging from several tens cm2/Vs to several hundreds cm2/Vs, it enables a data driving circuit or other peripherals requiring high electron mobility to be incorporated in a substrate. Further, the size of a polycrystalline silicon TFT is small, and thus the aperture ratio of a screen may be increased. In addition, since a driving circuit is incorporated in a substrate, there is no limit on line pitch for connecting the driving circuits as more pixels are disposed. As a result, high resolution may be achieved, driving voltage and power consumption may be saved, and deterioration of elements may be greatly suppressed.
As a technology to produce a polycrystalline silicon TFT, excimer laser crystallization (“ELC”) technique that crystallizes amorphous silicon to form polycrystalline silicon is under development. In this regard, in order to control a polycrystalline silicon TFT produced through such a crystallization process, it is important to check when the crystallization direction is uniform and when there is a bump such as a protrusion or a bank.
Unfortunately, it is difficult to observe crystallinity of polycrystalline silicon with the naked eyes and there is a limit on an error margin, and thus it is necessary to determine the crystalline direction of polycrystalline silicon. Under the circumstances, what is required is a device for evaluating crystallinity.